This week dangerous smog caused one of northeastern China’s biggest cities to be shut down by the government. Changhua Wu, our Greater China Director suggests this is a warning to Chinese and international leaders to take urgent action towards tacking climate change, weeks before COP19 begins in Warsaw, Poland.

It is recommended that an index measurement of PM2.5 (or particulate matter) should not rise above 300, because toxicity at this level in the atmosphere is extremely dangerous to human beings. Yet in Harbin, a city in the northeastern Chinese province of Heilongjiang, last Monday it hit 1,000.

Around 11 million people live in Harbin. The new reading immediately affected all of these people. Visibility was reduced to 10 meters. Public transport, roads, airports, schools and shops were closed.

But while the blanket of smog has begun to lift now, the cloudy dialogue around dangerous pollution levels aggravated by climate change remains.

Practice shows that for real improvements to be made by our government in environmental quality, we need the full participation of the general public. And with these now regular pollution headlines and the obvious spotlight on human health effects, this is firmlya public issue.

It is imperative that government and businesses respond to the public demand that something is done about our cities' pollution problems. Reducing and mitigating the impacts of pollution on human health should certainly be central to any government action. But leaders must also account for economic impacts - to minimize productivity damage and economic losses - because these have associated social issues too. The overriding impetus to act also comes from China's economic growth: rapid urbanization, population growth and urban land scarcity will further accelerate pollution and its health hazards.

Where should the government begin in this urgent task? Of course tackling sources of pollution in individual cities is very important, but China's fossil fuel-based energy structure is the country's largest source of air pollution. So in order to effectively address the wide-spread pollution challenge in China, a fundamental shift from our heavy reliance on coal to clean energy must happen. Removal of subsidies to fossil fuels must simultaneously be examined and implemented in China in the very near future.

The country has already made some great strides in the areas of environment and clean energy. In Beijing, our recently launched Clean Air Plan looks like it could raise the threshold of environmental protection and tackle the city's pollution, if we act on this plan now.

I also applaud the recent intensive actions taken by the municipal government to adopt a more integrated approach to tackle the PM 2.5 challenge through its control of vehicular pollution - one of the biggest priorities for the city of Beijing in addressing its notorious air pollution.

But in some areas we are stalling. Despite new subsidies, the electric vehicle industrial sector in China continues to face some technological barriers to overcome before scale up. Infrastructure to accommodate EV charging remains at the piloting stages. To address those barriers, sharing and learning from other countries' experiences is critical. China must more actively reach out to other countries for collaboration.

While it may be a long and difficult road to invest fully in clean energy, when we acquire the joint efforts of all countries, and focus on addressing issues of great public concern such as pollution, we will achieve great progress.

As we approach COP19 in Warsaw, China's leaders must set out to show real leadership on climate change.